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Old 9th Aug 2014, 9:15 pm   #81
John_BS
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Default Re: My Homebrew ESR Meter for testing el caps

I'll put money on the Tant.

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Old 10th Aug 2014, 12:20 pm   #82
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Default Re: My Homebrew ESR Meter for testing el caps

I didnt know the tantal needs polarity, so i reversed it and checked all solder points, but still nothing on the meter. However now i get good +5V on the 78L05.
Maybe i fried some other parts? Should i try another IC?
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Old 10th Aug 2014, 4:40 pm   #83
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Default Re: My Homebrew ESR Meter for testing el caps

There have been so many posts over the four years that this project has been rolling along that it might be helpful to reiterate some fault-finding pointers, and how the circuit operates.

The range of things that can cause the unit to not work is more or less limited to the following:

1) Faulty components (Notably the IC, transistor, tant cap, voltage regulator) or wrong component values.
2) Wrong orientation of polarity-sensitive components such as diodes, IC, transistor, tant cap, voltage regulator.
3) Short or open circuits.
4) Wiring errors.

Firstly, even if the unit isn't faulty you wont get any deflection on the meter or any input signal into the base of Q1 unless the test leads are shorted, so in carrying out checks, keep the leads shorted.

As to whether you may have damaged the 74HC14N, it is designed for a power supply range of 2.0V to 6.0V, so if its had more that 6V at pin 14, then yes, you may have zapped it. The only way of knowing would be to try it in a working piece of equipment, so you'll need to try a new one. Id suggest that you check that you have 5V+ at pin 14 of IC1, which you should have as you say you now have 5V at the output of the voltage regulator. If not, is there 9V at the input of the voltage regulator? If so, suspect the regulator. Check that you've used the right IC - 74HC14N. (Not 74HCT14N).

Also, there are two case styles of 2N222A with differing pin-outs so make sure the transistors is correctly wired. (See the diagram showing the two case styles).

Are all the diodes the right way round?

Are all the component values correct?

It helps if a 'scope is to hand to check the waveform at various points, and to gain an understanding of the various elements of the circuit and to pinpoint any malfunctions. The IC is a hex Schmidt trigger. One of the six gates, along with C1 and R1 form an oscillator circuit, which is as simple as an oscillator gets - a gate, a cap, a resistor! The values of C1 and R1 determine the oscillator frequency, which the designer states as 150 or 156kHz, but is in fact nearer to 100KHZ, though this isnt critical and has no bearing on the accuracy of the meter.

Pin 2 of the IC is the output of the oscillator, so you should see a square wave of about 4V p-p as shown in the first pic.

This square wave then goes to the input of the other five gates on the I.C. at pins 3,5,9,11 & 13. The outputs of those five gates at pins 4,6,8,10 & 12 go to the five 680 Ohm resistors R2,3,4,5 & 6, and form a buffer and Low Pass filter. At the junction of those resistors - which are all coupled together on their outputs - there should be a waveform of approximately 250mv peak to peak at about 100KHz, as shown in the second pic.

The next stage is the input protection stage (D5, D6, C5 etc) which protects the meter from damage should it get zapped with an un-discharged capacitor attached to the test leads.

From the junction of R8, D5, D6 and C5, there should be a waveform of about 180mV peak to peak, but its important to note that this is only when the test leads are shorted, or a good cap with a low ESR is connected to them. This AC waveform then passes via C2 to the base of the 2N2222A which is an AC amplifier with a gain of approx 10.5. It's role in life is to raise the 180mV p-p input to nearer 2 Volts p-p, depending on the gain of the individual transistor. See the third scope trace. If you see a 180mV waveform at the base of Q1 but nothing at the collector, suspect the transistor.

This waveform of 2V p-p or thereabouts from Q1 then passes to the meter rectifier D1,2,3 &4, for the meter movement. But without the test leads shorted, or a known good electrolytic cap with a low ESR attached to the test leads there will be zero Volts at the input of the 2N2222A, nothing at its output, so no deflection on the meter.

None of this will make any sense at all without being read alongside the circuit, so I've attached an updated circuit and notes which I drew up early in 2013 to incorporate the modifications that I've made over time to the original circuit, which might make it a bit easier to trace faults. My own approach to fault tracing on any equipment is to go over the circuit with a highlighter pen to highlight the parts that I've tested and verified are working.

Hope that helps a bit.

Good luck with the project.
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Old 10th Aug 2014, 5:18 pm   #84
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Default Re: My Homebrew ESR Meter for testing el caps

hello David

unfortunately i have no oscilloscope at hand. Is there anything i can measure with multimeter? 2n222 voltage output?

Parts i used 2x 1N4007 diodes instead 1N4004 and i replaced the old c547c against a 2n2222a which i checked emitter,base,collector.

Polarity should be fine on all the parts now, only tantal was a problem.
All other caps should not need polarity from my undestanding.

Now i even tried a second IC, still the same. With shortened test leads.

I dont even know if the meter works, it was new but who know if it works. It is 100µA, so the model should be ok. I dont know if my multimeter is able to measure such low currents.

Battery is a bit low at 8,5v but i get stable 5v output on the 78L05 and on pin14.
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Old 10th Aug 2014, 7:20 pm   #85
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Default Re: My Homebrew ESR Meter for testing el caps

Sorry to hear of your continued hassles - it's very disheartening when projects don't work - we've all been there.

To answer your queries in turn:

1) The problem in measuring voltage is that what we're looking at is AC waveforms of 100kHz or so - not DC voltages, so you'd need to use a multi-meter capable of measuring the p-p voltage of that AC waveform. I think that a typical multi-meter on its AC ranges is probably only designed to measure AC sine wave voltages of 50/60 Hz, but that depends on the meter spec. You could, I suppose, use a simple RF probe to convert the AC waveform to DC, and although it wouldn't be very accurate, at least it would show if the 100kHz waveform is present, certainly at pin 2 of the IC (approx. 4V p-p) and at the collector of the transistor (approx. 2V p-p). But that would side-track you into having to make a little RF probe. EG:

http://highfields-arc.co.uk/construc...ircuit/rfd.htm

Some more RF probe circuits here:

https://www.google.co.uk/search?q=si...tm%3B716%3B276


2) 1N4007s will be fine in place of 1N4004.

3) You can test the meter by applying 5V or so with a resistor of say 330k in series to protect the meter needle from 'end-stopping'.

4) The battery voltage being a bit low won't be a problem. (The IC will work down to 2V).

The only thing I can add is that a large number of these little units have been built over the course of the last four years or so and if built correctly, aren't temperamental, work first time and carry on working. All I can suggest is that you print off the circuit, and go through it a step at a time, checking each component (resistor values, caps etc) marking the circuit with a highlighter pen at each step of the way, using a magnifying glass to look for any short or open circuits or wiring errors, which is always a risk when using strip-board.

Hope that helps a bit.
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Old 10th Aug 2014, 8:19 pm   #86
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Default Re: My Homebrew ESR Meter for testing el caps

I hooked up the meter with 240k series to the 9v battery and got 40µA, so that should be fine i guess.

On the pcb i used an 25k pot instead R17 and there is no additional pot connected to the 100µA meter, i guess this is ok.

Maybe the tantal is still a problem but i have only normal caps here. However i see that topcap used an electrolyte, maybe worth a try.
Also i guess i am not the first one you used topcaps veroboard layout without resistor network.
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Old 10th Aug 2014, 9:08 pm   #87
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Default Re: My Homebrew ESR Meter for testing el caps

Quote:
Originally Posted by xrated2 View Post
I hooked up the meter with 240k series to the 9v battery and got 40A, so that should be fine i guess.
On the pcb i used an 25k pot instead R17 and there is no additional pot connected to the 100A meter, i guess this is ok.

1) Yes, the meter should be fine, but I've only just noticed that you've used a 100uA meter instead of the specified 50uA so even if the project works, you won't get full scale deflection on the meter - that is to say the meter needle won't go right across to the right (zero Ohms) with the test leads shorted, or with a capacitor under test which has a very low ESR. If indeed the needle does go right across to zero ohms, the scale will be very cramped towards the right hand end, which is where you want the scale to be expanded.

With the correct 50uA meter, 2 Ohms should be about 75 of FSD, 5 Ohms should be about 50% FSD, and 10 Ohms should be about 25% FSD. (See the attached scale).
You need the scale to be as wide as possible at the right hand end because if you can't read say 0.5 to 2 Ohms with reasonable accuracy, then really, the meter isn't much use.

2) It's OK to use the 25k pot and no R17 as long as you put a wire link in place of R17.
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Old 11th Aug 2014, 10:12 am   #88
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Default Re: My Homebrew ESR Meter for testing el caps

That it what Top Cap wrote:

"Having a spare RS 259-561 100uA edge-meter I used this though I had to leave out R17 to get enough meter drive, still using a 22k series pot for setting zero."

So iI just put a 25k pot instead of R17 in the same place.

If iI put a link on R17 place the meter will deflect! But why it won't work with the 25k pot?
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Old 11th Aug 2014, 10:41 am   #89
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Default Re: My Homebrew ESR Meter for testing el caps

Now i get confused, before i probably linked wrong places because i used only my hands and a piece of wire and prolly came on wrong pads. Thinking it was the pot, but i was misleaded.
But now i realised, if i link those 2 wrong ones together, the meter will deflect. I have marked it in the picture with a red line. If i do link like the red line, it will work.
R17 is currently linked by soldered wire.

But i dont understand why it works now. Something wrong with C6 or the 4 small diodes?
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Old 12th Aug 2014, 9:19 pm   #90
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Default Re: My Homebrew ESR Meter for testing el caps

or see here, easier to check
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Old 12th Aug 2014, 10:38 pm   #91
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Default Re: My Homebrew ESR Meter for testing el caps

Just check the diodes are all correctly placed, including polarity.
D3 Cathode should connect with D1 Cathode
D4 Anode should connect with D2 Anode
D1 Anode connects with D2 Cathode.
Also make sure your potentiometer is wired correctly and not interfering with the diode circuitry.
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Old 12th Aug 2014, 10:52 pm   #92
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Default Re: My Homebrew ESR Meter for testing el caps

hello

the mark on the diode (-) i have put to bottom side.
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Old 13th Aug 2014, 2:34 pm   #93
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Default Re: My Homebrew ESR Meter for testing el caps

Have also measured d1 and d2, both are ok. One direction 600mV, the other one nothing. Type T4148.
Everything is connected like in the layout, i dont understand where is the problem.
The pot on r17 location was bridged too.
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Old 13th Aug 2014, 3:31 pm   #94
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Default Re: My Homebrew ESR Meter for testing el caps

This is what i came up on the 100µA meter:

bridged 100
2,2r 95
8,2r 73
10r 60
27r 23
open 0

But only works when i bridge D1 and D2
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Old 13th Aug 2014, 6:11 pm   #95
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Default Re: My Homebrew ESR Meter for testing el caps

I had an open circuit pot on one meter I built - it was brand new. I tried another one of the same make/batch and this one was seized up at 25k.A third working 25k pot wouldn't give FSD; I ended up using a 10k in the end which did the job.

My first meter wouldn't work but I'm glad I persevered. Having built four now I've about got the hang of it.

Andy.
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Old 13th Aug 2014, 7:35 pm   #96
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Default Re: My Homebrew ESR Meter for testing el caps

Sorry to hear of your continued difficulties.

I can only say that if the circuit is correctly wired, with the correct value of components correctly orientated, and with the specified 50uA meter, there is no reason why it wouldn’t work, but of course you do need to take extra care with a strip-board version as the scope for errors is greater, as with any strip-board project. As to D1,2,3 & 4, they comprise the meter rectifier and if the diodes are wired as shown in the circuit, any AC voltage appearing at the rectifier should be rectified to DC and the meter should deflect, but if two of the diodes are shorted out, you are effectively re-designing rectifier the circuit.

Once more, these notes will only make any sense if read alongside the circuit:

Just to re-state how that part of the circuit works:

The AC waveform passes via C2 to the base of the 2N2222A, which is an AC amplifier which raises the 180mV p-p input at the base to nearer 2 Volts p-p at the collector. C3 blocks DC voltage from R11, while allowing the AC from the collector to pass to D1,2,3 &4, the meter rectifier, which - (just as in any analogue test meter designed to measure an AC voltage - an AVO for example) - rectifies the AC voltage to DC for the meter movement.

The lower the ESR of a capacitor under test, (or if the test leads are shorted), the higher will be the AC voltage (at approx 100kHz frequency) which is rectified to DC to deflect the meter needle. The worse the ESR, the lower will be the AC voltage into the rectifier, so the lower will be the deflection on the meter needle from the left to the right. (If the ESR is higher than about 75 Ohms, there will be no voltage at all appearing at the meter rectifier, so no DC to deflect the meter needle, but we're only interested in the low Ohms end of the scale, up to say 10 Ohms at most).

The specified meter is 50uA. Such meters are widely available on e-bay from Hong Kong for under £5.00 GBP post free (about 6.5 Euro). One supplier presently offers a 50uA meter with a large 10 x 8cm (3.9" x 3.1”) dial for £4.78 (6 Euro) post free. Though a 100uA meter will work after a fashion, and though I haven't tried to use a 100uA meter to see how it would work, it's my guess that it will be cramped at the low ESR end, (R.H. end) of the scale and that's exactly the end where we need the scale to be expanded as much as possble. It's important to understand that it isn’t simply a matter of getting the meter to go to full scale deflection with the test leads shorted by fiddling with the pre-set resistor or R17 or shorting R17 out. What is needed is to get the meter to deflect to the left to measure ESR.

To my mind, it hardly seems worth going to the trouble to build a test instrument if its performance is barely adequate because the wrong meter movement has been used.

Best wishes for a successful outcome!
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Old 13th Aug 2014, 7:42 pm   #97
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Default Re: My Homebrew ESR Meter for testing el caps

Quote:
Originally Posted by xrated2 View Post
hello the mark on the diode (-) i have put to bottom side.
The mark on the diode, usually a coloured band, denotes the Cathode and is usually shown as the + end following conventional current. On the layout drawing D3 and D4 cathodes are clearly shown by the dark bands at one end. Both D1 and D2 in the positions shown, should have their bands at the top (being mounted vertical).
Because you have your diodes inverted at this position, then the ends with the band should be close to the board.
Try re-mountin the diodes the correct way with their cathodes (banded ends) connected as shown by the +, i.e. both diodes fitted with their bands uppermost.
Les
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Old 13th Aug 2014, 8:41 pm   #98
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Default Re: My Homebrew ESR Meter for testing el caps

iI think we are getting close, iI am not am expert but iI thought it's like in the picture attached. But iI remember something like technical and electrical current
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Old 13th Aug 2014, 9:32 pm   #99
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Default Re: My Homebrew ESR Meter for testing el caps

Quote:
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i think we are getting close, i am not am expert but i thought its like in the picture attached.

But i remember something like technical and electrical current

No, the diodes should be the other way around. The Positive is the coloured band
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Old 13th Aug 2014, 10:04 pm   #100
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Default Re: My Homebrew ESR Meter for testing el caps

xrated2's drawing is correct. The marked end of the diode is the cathode. If the diode is used in a rectifier circuit, the cathode (marked end) will be the positive side of the DC output.
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